Hydrothermal-mechanical conversion of lignocellulosic biomass to ethanol or other fermentation products

ABSTRACT

A low-cost process is provided to render lignocellulosic biomass accessible to cellulase enzymes, to produce fermentable sugars. Some variations provide a process to produce ethanol from lignocellulosic biomass (such as sugarcane bagasse or corn stover), comprising introducing a lignocellulosic biomass feedstock to a single-stage digestor; exposing the feedstock to a reaction solution comprising steam or liquid hot water within the digestor, to solubilize the hemicellulose in a liquid phase and to provide a cellulose-rich solid phase; refining the cellulose-rich solid phase, together with the liquid phase, in a mechanical refiner, thereby providing a mixture of refined cellulose-rich solids and the liquid phase; enzymatically hydrolyzing the mixture in a hydrolysis reactor with cellulase enzymes, to generate fermentable sugars; and fermenting the fermentable sugars to produce ethanol. Many alternative process configurations are described. The disclosed processes may be employed for other fermentation products.

PRIORITY DATA

This patent application is a continuation application of U.S. patentapplication Ser. No. 15/047,608, filed Feb. 18, 2016, which claimspriority to U.S. Provisional Patent App. No. 62/118,335, filed Feb. 19,2015; U.S. Provisional Patent App. No. 62/141,664, filed Apr. 1, 2015;U.S. Provisional Patent App. No. 62/150,643, filed Apr. 21, 2015; U.S.Provisional Patent App. No. 62/197,160, filed Jul. 27, 2015; U.S.Provisional Patent App. No. 62/240,461, filed Oct. 12, 2015; U.S.Provisional Patent App. No. 62/263,292, filed Dec. 4, 2015; and U.S.Provisional Patent App. No. 62/267,533, filed Dec. 15, 2015, each ofwhich is hereby incorporated by reference herein.

FIELD OF THE INVENTION

The present invention generally relates to processes for preparingfermentable sugars and fermentation products from lignocellulosicbiomass.

BACKGROUND OF THE INVENTION

Lignocellulosic biomass is the most abundant renewable material on theplanet and has long been recognized as a potential feedstock forproducing chemicals, fuels, and materials. Lignocellulosic biomassnormally comprises primarily cellulose, hemicellulose, and lignin.Cellulose and hemicellulose are natural polymers of sugars, and ligninis an aromatic/aliphatic hydrocarbon polymer reinforcing the entirebiomass network.

Biomass refining (or biorefining) has become prevalent in the world'seconomy. Cellulose fibers and sugars, hemicellulose sugars, lignin,syngas, and derivatives of these intermediates are being utilized forchemical and fuel production. Integrated biorefineries are capable ofprocessing incoming biomass much the same as petroleum refineries nowprocess crude oil. Underutilized lignocellulosic biomass feedstocks havethe potential to be much cheaper than petroleum, on a carbon basis, aswell as much better from an environmental life-cycle standpoint. Overthe past few years, several commercial-scale biorefineries have beenconstructed, designed to convert lignocellulosic biomass such as cornstover, wheat straw, and sugarcane bagasse or straw into so-calledsecond-generation ethanol.

However, there remains a need for improved conversion technologies toproduce second-generation ethanol. What is needed is a low-cost,practical approach to render lignocellulosic biomass easily accessibleto cellulase enzymes, to produce fermentable sugars.

SUMMARY OF THE INVENTION

The present invention addresses the aforementioned needs in the art.Some variations of the invention are known as GreenPower3+® technologyor GP3+® technology, commonly assigned with the assignee of this patentapplication.

Some variations provide a process to produce a fermentation product(e.g., ethanol) from lignocellulosic biomass, the process comprising:

(a) introducing a lignocellulosic biomass feedstock to a single-stagedigestor, wherein the feedstock contains cellulose, hemicellulose, andlignin;

(b) exposing the feedstock to a reaction solution comprising steam orliquid hot water within the digestor, to solubilize at least a portionof the hemicellulose in a liquid phase and to provide a cellulose-richsolid phase;

(c) refining the cellulose-rich solid phase, together with the liquidphase, in a mechanical refiner to reduce average particle size of thecellulose-rich solid phase, thereby providing a mixture comprisingrefined cellulose-rich solids and the liquid phase;

(d) enzymatically hydrolyzing the mixture in a hydrolysis reactor withcellulase enzymes, to generate fermentable sugars from the mixture,wherein the hydrolysis reactor includes one or more hydrolysis stages;and

(e) fermenting at least some of the fermentable sugars in a fermentor toproduce a fermentation product.

In some embodiments, the lignocellulosic biomass feedstock is selectedfrom the group consisting of hardwoods, softwoods, sugarcane bagasse,sugarcane straw, energy cane, corn stover, corn cobs, corn fiber, andcombinations thereof.

The lignocellulosic biomass feedstock may be pretreated, prior to step(a), using one or more techniques selected from the group consisting ofcleaning, washing, presteaming, drying, milling, particlesize-classifying, and combinations thereof.

In some embodiments, the reaction solution further comprises an acid,such as (but not limited to) acetic acid. In some embodiments, at leasta portion of the reaction solution is introduced to the feedstock in apre-impregnator prior to step (b).

Step (b) may include a digestor residence time from about 2 minutes toabout 4 hours. In some embodiments, the digestor residence time is about10 minutes or less. Step (b) may include a digestor temperature fromabout 150° C. to about 220° C., such as from about 180° C. to about 200°C. Step (b) may be conducted at a digestor liquid-solid weight ratiofrom about 1 to about 4, preferably about 2 or less. Step (b) may beconducted at a digestor pH from about 3 to about 5, such as from about3.5 to about 4.5.

In some embodiments of the process, a blow tank is configured forreceiving the cellulose-rich solid phase or the refined cellulose-richsolids at a pressure lower than the digestor pressure. The blow tank maybe disposed downstream of the digestor and upstream of the mechanicalrefiner, i.e. between the digestor and refiner. Or the blow tank may bedisposed downstream of the mechanical refiner. In certain embodiments, afirst blow tank is disposed upstream of the mechanical refiner and asecond blow tank is disposed downstream of the mechanical refiner.Optionally, vapor is separated from the blow tank(s). The vapor may bepurged and/or condensed or compressed and returned to the digestor. Ineither case, heat may be recovered from at least some of the vapor.

The mechanical refiner may be selected from the group consisting of ahot-blow refiner, a hot-stock refiner, a blow-line refiner, a diskrefiner, a conical refiner, a cylindrical refiner, an in-linedefibrator, an extruder, a homogenizer, and combinations thereof.

The mechanical refiner may be operated at a refining pressure selectedfrom about 1 bar to about 20 bar. In some embodiments, the refiningpressure is about 3 bar or less. In some embodiment, the mechanicalrefiner is operated at or about at atmospheric pressure.

The mechanical refiner may operate at an electrical load from about 2 kWto about 50 kW, such as from about 5 kW to about 20 kW, refining powerper ton of the cellulose-rich solid phase. The mechanical refiner maytransfer up to about 500 kW-hr refining energy per ton of thecellulose-rich solid phase, such as from about 50 kW-hr to about 200kW-hr refining energy per ton of the cellulose-rich solid phase.

The process may utilize multiple mechanical refiners at different partsof the process. For example, between steps (c) and (d), at least aportion of the mixture may be conveyed to a second mechanical refiner,typically operated at the same or a lower refining pressure compared tothat of the mechanical refiner in step (c). In certain embodiments, thefirst mechanical refiner in step (c) is a pressurized refiner and thesecond mechanical refiner is an atmospheric refiner.

In some embodiments, step (d) utilizes multiple enzymatic-hydrolysisreactors. For example, step (d) may utilize single-stage enzymatichydrolysis configured for cellulose liquefaction and saccharification,wherein the single-stage enzymatic hydrolysis includes one or more tanksor vessels. Step (d) may utilize multiple-stage enzymatic hydrolysisconfigured for cellulose liquefaction followed by saccharification,wherein each stage includes one or more tanks or vessels. Whenmultiple-stage enzymatic hydrolysis is employed, the process may includeadditional mechanical refining of the mixture, or a partially hydrolyzedform thereof, following at least a first stage of enzymatic hydrolysis.

The process according to some embodiments further includes:

introducing the mixture to a first enzymatic-hydrolysis reactor undereffective hydrolysis conditions to produce a liquid hydrolysatecomprising sugars from the refined cellulose-rich solids and optionallyfrom the hemicellulose, and a residual cellulose-rich solid phase;

optionally separating at least some of the liquid hydrolysate from theresidual cellulose-rich solid phase;

conveying the residual cellulose-rich solid phase through an additionalmechanical refiner and/or recycling the residual cellulose-rich solidphase through the mechanical refiner, to generate refined residualcellulose-rich solids; and

introducing the refined residual cellulose-rich solids to a secondenzymatic-hydrolysis reactor under effective hydrolysis conditions, toproduce additional sugars.

In some embodiments, a self-cleaning filter is configured downstream ofthe hydrolysis reactor to remove cellulosic fiber strands. Thecellulosic fiber strands may be recycled back to the hydrolysis reactor.

Cellulase enzymes may be introduced directly to the mechanical refiner,so that simultaneous refining and hydrolysis occurs. Alternatively, oradditionally, cellulase enzymes may be introduced to the cellulose-richsolid phase prior to step (c), so that during step (c), simultaneousrefining and hydrolysis occurs. In these embodiments, the mechanicalrefiner is preferably operated at a maximum temperature of 75° C. orless to maintain effective hydrolysis conditions.

The process may include conversion of hemicellulose to the fermentationproduct, in various ways. For example, step (d) may include enzymatichydrolysis of hemicellulose oligomers to generate fermentable monomersugars. Step (e) may include enzymatic hydrolysis of hemicelluloseoligomers to generate fermentable monomer sugars within the fermentor.The monomer sugars, derived from hemicellulose, may be co-fermentedalong with glucose or may be fermented in a second fermentor operated inseries or parallel with the primary fermentor.

The process may further comprise removal of one or more fermentationinhibitors, such as by steam stripping. In some embodiments, acetic acid(a fermentation inhibitor) is removed and optionally recycled to thedigestor.

The process typically includes concentrating the fermentation product bydistillation. The distillation generates a distillation bottoms stream,and in some embodiments the distillation bottoms stream is evaporated ina distillation bottoms evaporator that is a mechanical vapor compressionevaporator or is integrated in a multiple-effect evaporator train.

The fermentation product may be selected from the group consisting ofethanol, isopropanol, acetone, n-butanol, isobutanol, 1,4-butanediol,succinic acid, lactic acid, and combinations thereof. In certainembodiments, the fermentation product is ethanol (and CO₂ necessarilyproduced in fermentation).

Other variations of the invention provide a process to produce afermentation product from lignocellulosic biomass, the processcomprising:

(a) introducing a lignocellulosic biomass feedstock to a digestor,wherein the feedstock contains cellulose, hemicellulose, and lignin;

(b) exposing the feedstock to a reaction solution comprising steam orliquid hot water within the digestor, to solubilize at least a portionof the hemicellulose in a liquid phase and to provide a cellulose-richsolid phase;

(c) separating at least a portion of the liquid phase from thecellulose-rich solid phase;

(d) mechanically refining the cellulose-rich solid phase to reduceaverage particle size, thereby providing refined cellulose-rich solids;

(e) enzymatically hydrolyzing the refined cellulose-rich solids in ahydrolysis reactor with cellulase enzymes, to generate fermentablesugars;

(f) hydrolyzing the hemicellulose in the liquid phase, separately fromstep (e), to generate fermentable hemicellulose sugars; and

(g) fermenting at least some of the fermentable sugars, and optionallyat least some of the fermentable hemicellulose sugars, in a fermentor toproduce a fermentation product.

Still other variations of the invention provide a process to produce afermentation product from lignocellulosic biomass, the processcomprising:

(a) introducing a lignocellulosic biomass feedstock to a digestor,wherein the feedstock contains cellulose, hemicellulose, and lignin;

(b) exposing the feedstock to a reaction solution comprising steam orliquid hot water within the digestor, to solubilize at least a portionof the hemicellulose in a liquid phase and to provide a cellulose-richsolid phase;

(c) mechanically refining the cellulose-rich solid phase to reduceaverage particle size, thereby providing refined cellulose-rich solidsmixed with the liquid phase;

(d) separating at least a portion of the liquid phase from the refinedcellulose-rich solids;

(e) enzymatically hydrolyzing the refined cellulose-rich solids in ahydrolysis reactor with cellulase enzymes, to generate fermentablesugars;

(f) hydrolyzing the hemicellulose in the liquid phase, separately fromstep (e), to generate fermentable hemicellulose sugars; and

(g) fermenting at least some of the fermentable sugars, and optionallyat least some of the fermentable hemicellulose sugars, in a fermentor toproduce a fermentation product.

Yet other variations of the invention provide a process to producefermentable sugars from lignocellulosic biomass, the process comprising:

(a) introducing a lignocellulosic biomass feedstock to a single-stagedigestor, wherein the feedstock contains cellulose, hemicellulose, andlignin;

(b) exposing the feedstock to a reaction solution comprising steam orliquid hot water within the digestor, to solubilize at least a portionof the hemicellulose in a liquid phase and to provide a cellulose-richsolid phase;

(c) mechanically refining the cellulose-rich solid phase, together withthe liquid phase, to reduce average particle size of the cellulose-richsolid phase, thereby providing a mixture comprising refinedcellulose-rich solids and the liquid phase;

(d) enzymatically hydrolyzing the mixture in a hydrolysis reactor withcellulase enzymes, to generate fermentable sugars from the mixture; and

(e) recovering or further treating the fermentable sugars.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a simplified block-flow diagram depicting the process of someembodiments of the present invention, employing a pressurized blow-linerefiner.

FIG. 2 is a simplified block-flow diagram depicting the process of someembodiments of the present invention, employing an atmospheric refiner.

FIG. 3 is a simplified block-flow diagram depicting the process of someembodiments of the present invention, employing multiple blow tanks witha pressurized refiner between the blow tanks.

FIG. 4 is a simplified block-flow diagram depicting the process of someembodiments of the present invention, employing an atmospheric refinerand lignin recovery.

FIG. 5 is a simplified block-flow diagram depicting the process of someembodiments of the present invention, employing an atmospheric refinerand integrated enzymatic or acid hydrolysis.

FIG. 6 is a simplified block-flow diagram depicting the process of someembodiments of the present invention, employing an atmospheric refinerand recycle of unconverted solids after enzymatic hydrolysis back to therefiner.

FIG. 7 is a simplified block-flow diagram depicting the process of someembodiments of the present invention, employing an atmospheric refinerand recycle of unconverted solids after solid-liquid separation back tothe refiner.

FIG. 8 is a simplified block-flow diagram depicting the integratedprocess of some embodiments of the present invention, with a pressurizedrefiner, intermediate hydrolysate evaporation, and concentration of thefermentation product.

FIG. 9 is a simplified block-flow diagram depicting the integratedprocess of some embodiments of the present invention, with an optionalmechanical refiner, intermediate hydrolysate evaporation, andconcentration of the fermentation product.

FIG. 10 is a simplified block-flow diagram depicting the process of someembodiments, employing additional refining and additional hydrolysissteps.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

This description will enable one skilled in the art to make and use theinvention, and it describes several embodiments, adaptations,variations, alternatives, and uses of the invention. These and otherembodiments, features, and advantages of the present invention willbecome more apparent to those skilled in the art when taken withreference to the following detailed description of the invention inconjunction with any accompanying drawings.

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” include plural referents unless the contextclearly indicates otherwise. Unless defined otherwise, all technical andscientific terms used herein have the same meaning as is commonlyunderstood by one of ordinary skill in the art to which this inventionbelongs. All composition numbers and ranges based on percentages areweight percentages, unless indicated otherwise. All ranges of numbers orconditions are meant to encompass any specific value contained withinthe range, rounded to any suitable decimal point.

Unless otherwise indicated, all numbers expressing reaction conditions,stoichiometries, concentrations of components, and so forth used in thespecification and claims are to be understood as being modified in allinstances by the term “about.” Accordingly, unless indicated to thecontrary, the numerical parameters set forth in the followingspecification and attached claims are approximations that may varydepending at least upon a specific analytical technique.

The term “comprising,” which is synonymous with “including,”“containing,” or “characterized by” is inclusive or open-ended and doesnot exclude additional, unrecited elements or method steps. “Comprising”is a term of art used in claim language which means that the named claimelements are essential, but other claim elements may be added and stillform a construct within the scope of the claim.

As used herein, the phrase “consisting of” excludes any element, step,or ingredient not specified in the claim. When the phrase “consists of”(or variations thereof) appears in a clause of the body of a claim,rather than immediately following the preamble, it limits only theelement set forth in that clause; other elements are not excluded fromthe claim as a whole. As used herein, the phrase “consisting essentiallyof” limits the scope of a claim to the specified elements or methodsteps, plus those that do not materially affect the basis and novelcharacteristic(s) of the claimed subject matter.

With respect to the terms “comprising,” “consisting of,” and “consistingessentially of,” where one of these three terms is used herein, thepresently disclosed and claimed subject matter may include the use ofeither of the other two terms. Thus in some embodiments not otherwiseexplicitly recited, any instance of “comprising” may be replaced by“consisting of” or, alternatively, by “consisting essentially of.”

Some variations are premised on the discovery of a simple process forconverting lignocellulosic biomass into fermentable sugars. In someembodiments, biomass is subjected to a steam or hot-water soak todissolve hemicelluloses, with or without acetic acid addition. This stepmay optionally be followed by mechanical refining, such as in a hot-blowrefiner, of the cellulose-rich (and lignin-rich) solids. The refinedsolids are then enzymatically hydrolyzed to generate sugars, in one ormore hydrolysis (or liquefaction) reactors or vessels. An evaporationstep following enzymatic hydrolysis, and prior to fermentation, may beincluded to remove water and potentially fermentation inhibitors fromthe hydrolysate. This intermediate evaporation reduces capital andoperating costs of a process for cellulosic biofuels, such as ethanoland butanol.

Cellulose accessibility to cellulase enzymes is achieved according tothe disclosed processes. The accessibility is maximized by using twocontrols that are (i) hydrothermal and (ii) mechanical in nature.Optimum hydrothermal conditions provide release of hemicelluloses fromthe biomass solid structure, which increases cellulose accessibility toenzymes, even when the lignin content remains high. Optimum mechanicalrefining conditions provide enhanced cellulose accessibility to enzymes.

Certain exemplary embodiments of the invention will now be described.These embodiments are not intended to limit the scope of the inventionas claimed. The order of steps may be varied, some steps may be omitted,and/or other steps may be added. Reference herein to first step, secondstep, etc. is for illustration purposes only. Similarly, unit operationsmay be configured in different sequences, some units may be omitted, andother units may be added.

FIGS. 1 to 10 present simplified block-flow diagrams depicting theprocess of some embodiments of the present invention. The process ofFIG. 1 employs a pressurized blow-line refiner. The process of employsan atmospheric refiner. The process of FIG. 3 employs multiple blowtanks with a pressurized refiner between the blow tanks. The process ofFIG. 4 employs an atmospheric refiner and lignin recovery. The processof FIG. 5 employs an atmospheric refiner and integrated enzymatic oracid hydrolysis. The process of FIG. 6 employs an atmospheric refinerand recycle of unconverted solids after enzymatic hydrolysis back to therefiner. The process of FIG. 7 employs an atmospheric refiner andrecycle of unconverted solids after solid-liquid separation back to therefiner. The process of FIG. 8 employs a pressurized refiner,intermediate hydrolysate evaporation, and concentration of thefermentation product. The process of FIG. 9 includes an optionalmechanical refiner, intermediate hydrolysate evaporation, andconcentration of the fermentation product. The process of FIG. 10employs (optionally) several additional refining and additionalhydrolysis steps.

Some variations provide a process to produce a fermentation product(e.g., ethanol) from lignocellulosic biomass, the process comprising:

(a) introducing a lignocellulosic biomass feedstock to a single-stagedigestor, wherein the feedstock contains cellulose, hemicellulose, andlignin;

(b) exposing the feedstock to a reaction solution comprising steam orliquid hot water within the digestor, to solubilize at least a portionof the hemicellulose in a liquid phase and to provide a cellulose-richsolid phase;

(c) refining the cellulose-rich solid phase, together with the liquidphase, in a mechanical refiner to reduce average particle size of thecellulose-rich solid phase, thereby providing a mixture comprisingrefined cellulose-rich solids and the liquid phase;

(d) enzymatically hydrolyzing the mixture in a hydrolysis reactor withcellulase enzymes, to generate fermentable sugars from the mixture,wherein the hydrolysis reactor includes one or more hydrolysis stages;and

(e) fermenting at least some of the fermentable sugars in a fermentor toproduce a fermentation product.

In some embodiments, the lignocellulosic biomass feedstock is selectedfrom the group consisting of hardwoods, softwoods, sugarcane bagasse,sugarcane straw, energy cane, corn stover, corn cobs, corn fiber, andcombinations thereof.

The biomass feedstock may be selected from hardwoods, softwoods, forestresidues, agricultural residues (such as sugarcane bagasse), industrialwastes, consumer wastes, or combinations thereof In any of theseprocesses, the feedstock may include sucrose. In some embodiments withsucrose present in the feedstock (e.g., sugarcane or sugar beets), amajority of the sucrose is recovered as part of the fermentable sugars.In some embodiments with dextrose (or starch that is readily hydrolyzedto dextrose) present in the feedstock (e.g., corn), the dextrose isrecovered as part of the fermentable sugars.

Some embodiments of the invention enable processing of “agriculturalresidues,” which for present purposes is meant to includelignocellulosic biomass associated with food crops, annual grasses,energy crops, or other annually renewable feedstocks. Exemplaryagricultural residues include, but are not limited to, corn stover, cornfiber, wheat straw, sugarcane bagasse, rice straw, oat straw, barleystraw, miscanthus, energy cane, or combinations thereof.

The lignocellulosic biomass feedstock may be pretreated, prior to step(a), using one or more techniques selected from the group consisting ofcleaning, washing, presteaming, drying, milling, particlesize-classifying, and combinations thereof. The process may includecleaning the starting feedstock by wet or dry cleaning. The process mayinclude size reduction, hot-water soaking, dewatering, steaming, orother operations, upstream of the digestor.

In some embodiments, the reaction solution further comprises an acid,such as (but not limited to) acetic acid. In some embodiments, at leasta portion of the reaction solution is introduced to the feedstock in apre-impregnator prior to step (b).

Step (b) may include a digestor residence time from about 2 minutes toabout 4 hours. In some embodiments, the digestor residence time is about10 minutes or less. In various embodiments, the digestor residence timeis about 15, 20, 25, 30, 35, 40, 45, 50, 55 minutes, or about 1.0, 1.5,2.0, 2.5, 3.0, 3.5, or 4.0 hours.

Step (b) may include a digestor temperature from about 150° C. to about220° C., such as from about 180° C. to about 200° C. In variousembodiments, the digestor temperature is about 160° C., 165° C., 170°C., 175° C., 180° C., 181° C., 182° C., 183° C., 184° C., 185° C., 186°C., 187° C., 188° C., 189° C., 190° C., 195° C., or 200° C. At a givenreaction severity, there is a trade-off between time and temperature.Optionally, a temperature profile is specified for the digestor.

It is noted that the digestor temperature may be measured in a varietyof ways. The digestor temperature may be taken as the vapor temperaturewithin the digestor. The digestor temperature may be measured from thetemperature of the solids and/or the liquids (or a reacting mixturethereof). The digestor temperature may be taken as the digestor inlettemperature, the digestor outlet temperature, or a combination orcorrelation thereof The digestor temperature may be measured as, orcorrelated with, the digestor wall temperature. Note that especially atshort residence times (e.g., 5 minutes), the temperatures of differentphases present vapor, liquid, solid, and metal walls) may not reachequilibrium.

Step (b) may include a digestor pressure from atmospheric pressure up toabout 40 bar, such as from about 10 bar to about 20 bar. The digestorpressure may correspond to the steam saturation pressure at the digestortemperature. In some embodiments, the digestor pressure is higher thanthe steam saturation pressure at the digestor temperature, such as whensupersaturated water vapor is desired, or when an inert gas is alsopresent in the digestor. In some embodiments, the digestor pressure islower than the steam saturation pressure at the digestor temperature,such as when superheated steam is desired, or when a digestor vaporbleed line is present.

Step (b) may be conducted at a digestor liquid-solid weight ratio fromabout 0.1 to about 10, such as from about 1 to about 4, preferably about2 or less. In various embodiments, the digestor liquid-solid weightratio is about 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0,2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, or 3.0.

Step (b) may be conducted at a digestor pH from about 2 to about 6, suchas from about 3 to 5, or from about 3.5 to about 4.5. In variousembodiments, the digestor pH is about 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7,3.8, 3.9, 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, or 4.9.Generally, a lower pH gives a higher reaction severity. Typically, thedigestor pH is not controlled but is dictated by the composition of thestarting feedstock (e.g., acid content or buffer capacity) and whetheran acid is included in the aqueous reaction solution. Based onmeasurements made to the starting material or dynamic measurements madeor correlated during the process, an additive (e.g., an acid or base)may be added to the digestor to vary the digestor pH.

In some embodiments of the process, a blow tank is configured forreceiving the cellulose-rich solid phase or the refined cellulose-richsolids at a pressure lower than the digestor pressure. The blow tank maybe disposed downstream of the digestor and upstream of the mechanicalrefiner, i.e. between the digestor and refiner. Or the blow tank may bedisposed downstream of the mechanical refiner. In certain embodiments, afirst blow tank is disposed upstream of the mechanical refiner and asecond blow tank is disposed downstream of the mechanical refiner.Optionally, vapor is separated from the blow tank(s). The vapor may bepurged and/or condensed or compressed and returned to the digestor. Ineither case, heat may be recovered from at least some of the vapor.

The mechanical refiner may be selected from the group consisting of ahot-blow refiner, a hot-stock refiner, a blow-line refiner, a diskrefiner, a conical refiner, a cylindrical refiner, an in-linedefibrator, an extruder, a homogenizer, and combinations thereof

The mechanical refiner may be operated at a refining pressure selectedfrom about 1 bar to about 20 bar. In some embodiments, the refiningpressure is about 3 bar or less. In some embodiment, the mechanicalrefiner is operated at or about at atmospheric pressure.

The mechanical refiner may operate at an electrical load from about 2 kWto about 50 kW, such as from about 5 kW to about 20 kW, refining powerper ton of the cellulose-rich solid phase. In various embodiments, themechanical refiner operates at an electrical load of about 3, 4, 5, 6,7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, or 40kW refining power per ton of the cellulose-rich solid phase.

The mechanical refiner may transfer up to about 500 kW-hr refiningenergy per ton of the cellulose-rich solid phase, such as from about 50kW-hr to about 200 kW-hr refining energy per ton of the cellulose-richsolid phase. In various embodiments, the mechanical refiner transfersabout 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150,160, 170, 180, 190, 200, 225, 250, 275, 300, 325, 350, or 400 kW-hrrefining energy per ton of the cellulose-rich solid phase.

The mechanical refiner may be designed and operating using principlesthat are well-known in the art of pulp and paper plants andbiorefineries. For example, refiner plate gap dimensions may be varied,such as from about 0.1 mm to about 10 mm, or about 0.5 mm to about 2 mm,to reach the desired particle-size distribution. The choice of gapdimensions may depend on the nature of the starting feedstock, forexample.

In some embodiments, the mechanical refiner is designed and/or adjustedto achieve certain average fiber lengths, such as about 1 mm, 0.9 mm,0.8 mm, 0.7 mm, 0.6 mm, 0.5 mm, 0.4 mm, 0.3 mm, 0.2 mm, 0.1 mm or less.Generally speaking, shorter fibers or fibers with lower diameter areeasier to enzymatically hydrolyze to sugars, compared to larger fibers.

In some embodiments, the mechanical refiner is designed and/or adjustedto achieve a certain shives (bundles of fibers) content, such as lessthan about 5%, 4%, 3%, 2%, 1%, 0.5%, or less. Shives are not desirablebecause they tend to be more difficult to enzymatically hydrolyze tosugars. Knots and other large particles should be refined as well.

The process may utilize multiple mechanical refiners at different partsof the process. For example, between steps (c) and (d), at least aportion of the mixture may be conveyed to a second mechanical refiner,typically operated at the same or a lower refining pressure compared tothat of the mechanical refiner in step (c). In certain embodiments, thefirst mechanical refiner in step (c) is a pressurized refiner and thesecond mechanical refiner is an atmospheric refiner.

In some embodiments, step (d) utilizes multiple enzymatic-hydrolysisreactors. For example, step (d) may utilize single-stage enzymatichydrolysis configured for cellulose liquefaction and saccharification,wherein the single-stage enzymatic hydrolysis includes one or more tanksor vessels. Step (d) may utilize multiple-stage enzymatic hydrolysisconfigured for cellulose liquefaction followed by saccharification,wherein each stage includes one or more tanks or vessels. Whenmultiple-stage enzymatic hydrolysis is employed, the process may includeadditional mechanical refining of the mixture, or a partially hydrolyzedform thereof, following at least a first stage of enzymatic hydrolysis.

In some embodiments, non-acid and non-enzyme catalysts may be employedfor co-hydrolyzing glucose oligomers and hemicellulose oligomers. Forexample, base catalysts, solid catalysts, ionic liquids, or othereffective materials may be employed.

The process according to some embodiments further includes:

introducing the mixture to a first enzymatic-hydrolysis reactor undereffective hydrolysis conditions to produce a liquid hydrolysatecomprising sugars from the refined cellulose-rich solids and optionallyfrom the hemicellulose, and a residual cellulose-rich solid phase;

optionally separating at least some of the liquid hydrolysate from theresidual cellulose-rich solid phase;

conveying the residual cellulose-rich solid phase through an additionalmechanical refiner and/or recycling the residual cellulose-rich solidphase through the mechanical refiner, to generate refined residualcellulose-rich solids; and

introducing the refined residual cellulose-rich solids to a secondenzymatic-hydrolysis reactor under effective hydrolysis conditions, toproduce additional sugars.

In some embodiments, a self-cleaning filter is configured downstream ofthe hydrolysis reactor to remove cellulosic fiber strands. Thecellulosic fiber strands may be recycled, at least in part, back to thehydrolysis reactor.

Cellulase enzymes may be introduced directly to the mechanical refiner,so that simultaneous refining and hydrolysis occurs. Alternatively, oradditionally, cellulase enzymes may be introduced to the cellulose-richsolid phase prior to step (c), so that during step (c), simultaneousrefining and hydrolysis occurs. In these embodiments, the mechanicalrefiner is preferably operated at a maximum temperature of 75° C., 70°C., 65° C., 60° C., 55° C., 50° C. or less to maintain effectivehydrolysis conditions.

The process may include conversion of hemicellulose to the fermentationproduct, in various ways. For example, step (d) may include enzymatichydrolysis of hemicellulose oligomers to generate fermentable monomersugars. Step (e) may include enzymatic hydrolysis of hemicelluloseoligomers to generate fermentable monomer sugars within the fermentor.The monomer sugars, derived from hemicellulose, may be co-fermentedalong with glucose or may be fermented in a second fermentor operated inseries or parallel with the primary fermentor.

The process may further comprise removal of one or more fermentationinhibitors, such as by steam stripping. In some embodiments, acetic acid(a fermentation inhibitor) is removed and optionally recycled to thedigestor.

The process typically includes concentrating the fermentation product bydistillation. The distillation generates a distillation bottoms stream,and in some embodiments the distillation bottoms stream is evaporated ina distillation bottoms evaporator that is a mechanical vapor compressionevaporator or is integrated in a multiple-effect evaporator train.

The fermentation product may be selected from the group consisting ofethanol, isopropanol, acetone, n-butanol, isobutanol, 1,4-butanediol,succinic acid, lactic acid, and combinations thereof. In certainembodiments, the fermentation product is ethanol (and CO₂ necessarilyco-produced in fermentation).

The solid yield (also known as pulp yield or fiber yield) is thefraction of solids remaining (not dissolved) following digestion andrefining, but prior to enzymatic hydrolysis, relative to the startingbiomass feedstock. The solid yield of the process may vary, such as fromabout 60% to about 90%, typically from about 70% to about 80%. The solidyield does not include dissolved solids (e.g., hemicellulose sugars insolution). In various embodiments, the solid yield is about 70%, 71%,72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, or 80%.

The sugar yield (also known as carbohydrate yield) is the fraction ofsugar monomers and oligomers following enzymatic hydrolysis, but priorto fermentation of the hydrolysate, relative to the solid materialentering hydrolysis from digestion and any refining. The sugar yield ofthe process may vary, such as from about 40% to about 80% (or more),preferably at least 50%. In various embodiments, the sugar yield isabout 50%, 52%, 54%, 56%, 58%, 60%, 62%, 64%, 66%, 68%, 70%, or more.

The fraction of starting hemicellulose that is extracted into solutionmay be from about 50% to about 95%, such as about 55%, 60%, 65%, 70%,75%, 80%, 85%, or 90%.

The fermentation product yield (e.g., ethanol yield) is the yield offinal product produced in fermentation, relative to the theoreticalyield if all sugars are fermented to the product. The theoreticalfermentation yield accounts for any necessary co-products, such ascarbon dioxide in the case of ethanol. In the case of ethanol, theethanol yield of the process may vary, such as from about 65% to about95%, typically at least 80%. In various embodiments, the ethanol yieldis about 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%,87%, 88%, 89%, 90% or more. An ethanol yield on the basis of startingfeedstock can also be calculated. In various embodiments, the ethanolyield is from about 45 gal/T (T is dry tons of starting lignocellulosicfeedstock) to about 85 gal/T, typically about 60 gal/T or more.

Other variations of the invention provide a process to produce afermentation product from lignocellulosic biomass, the processcomprising:

(a) introducing a lignocellulosic biomass feedstock to a digestor,wherein the feedstock contains cellulose, hemicellulose, and lignin;

(b) exposing the feedstock to a reaction solution comprising steam orliquid hot water within the digestor, to solubilize at least a portionof the hemicellulose in a liquid phase and to provide a cellulose-richsolid phase;

(c) separating at least a portion of the liquid phase from thecellulose-rich solid phase;

(d) mechanically refining the cellulose-rich solid phase to reduceaverage particle size, thereby providing refined cellulose-rich solids;

(e) enzymatically hydrolyzing the refined cellulose-rich solids in ahydrolysis reactor with cellulase enzymes, to generate fermentablesugars;

(f) hydrolyzing the hemicellulose in the liquid phase, separately fromstep (e), to generate fermentable hemicellulose sugars; and

(g) fermenting at least some of the fermentable sugars, and optionallyat least some of the fermentable hemicellulose sugars, in a fermentor toproduce a fermentation product.

Still other variations of the invention provide a process to produce afermentation product from lignocellulosic biomass, the processcomprising:

(a) introducing a lignocellulosic biomass feedstock to a digestor,wherein the feedstock contains cellulose, hemicellulose, and lignin;

(b) exposing the feedstock to a reaction solution comprising steam orliquid hot water within the digestor, to solubilize at least a portionof the hemicellulose in a liquid phase and to provide a cellulose-richsolid phase;

(c) mechanically refining the cellulose-rich solid phase to reduceaverage particle size, thereby providing refined cellulose-rich solidsmixed with the liquid phase;

(d) separating at least a portion of the liquid phase from the refinedcellulose-rich solids;

(e) enzymatically hydrolyzing the refined cellulose-rich solids in ahydrolysis reactor with cellulase enzymes, to generate fermentablesugars;

(f) hydrolyzing the hemicellulose in the liquid phase, separately fromstep (e), to generate fermentable hemicellulose sugars; and

(g) fermenting at least some of the fermentable sugars, and optionallyat least some of the fermentable hemicellulose sugars, in a fermentor toproduce a fermentation product.

Yet other variations of the invention provide a process to producefermentable sugars from lignocellulosic biomass, the process comprising:

(a) introducing a lignocellulosic biomass feedstock to a single-stagedigestor, wherein the feedstock contains cellulose, hemicellulose, andlignin;

(b) exposing the feedstock to a reaction solution comprising steam orliquid hot water within the digestor, to solubilize at least a portionof the hemicellulose in a liquid phase and to provide a cellulose-richsolid phase;

(c) mechanically refining the cellulose-rich solid phase, together withthe liquid phase, to reduce average particle size of the cellulose-richsolid phase, thereby providing a mixture comprising refinedcellulose-rich solids and the liquid phase;

(d) enzymatically hydrolyzing the mixture in a hydrolysis reactor withcellulase enzymes, to generate fermentable sugars from the mixture; and

(e) recovering or further treating the fermentable sugars.

In some variations, a process is provided for producing fermentablesugars from cellulosic biomass, the process comprising:

(a) providing a feedstock comprising cellulosic biomass;

(b) digesting the feedstock with a reaction solution including steamand/or hot water in a digestor under effective reaction conditions toproduce a digested stream containing cellulose-rich solids,hemicellulose oligomers, and lignin;

(c) conveying the digested stream through a mechanical refiner, therebygenerating a refined stream with reduced average particle size of thecellulose-rich solids;

(d) separating a vapor from the refined stream;

(e) introducing the refined stream to an enzymatic hydrolysis unit undereffective hydrolysis conditions to produce sugars from thecellulose-rich solids and optionally from the hemicellulose oligomers;and

(f) recovering or further processing at least some of the sugars asfermentable sugars.

Some variations provide a process for producing fermentable sugars fromcellulosic biomass, the process comprising:

(a) providing a feedstock comprising cellulosic biomass;

(b) digesting the feedstock with a reaction solution including steamand/or hot water in a digestor under effective reaction conditions toproduce a digested stream containing cellulose-rich solids,hemicellulose oligomers, and lignin;

(c) conveying the digested stream through a mechanical refiner, therebygenerating a refined stream with reduced average particle size of thecellulose-rich solids;

(d) separating a vapor from the refined stream;

(e) introducing the refined stream to an acid hydrolysis unit undereffective hydrolysis conditions to produce sugars from thecellulose-rich solids and optionally from the hemicellulose oligomers;

(f) recovering or further processing at least some of the sugars asfermentable sugars.

Certain embodiments provide a process for producing ethanol fromcellulosic biomass, the process comprising:

(a) providing a feedstock comprising cellulosic biomass;

(b) digesting the feedstock with a reaction solution including steamand/or hot water in a digestor under effective reaction conditions toproduce a digested stream containing cellulose-rich solids,hemicellulose oligomers, and lignin;

(c) conveying the digested stream through a blow-line refiner, therebygenerating a refined stream with reduced average particle size of thecellulose-rich solids;

(d) separating a vapor from the refined stream;

(e) introducing the refined stream to an enzymatic hydrolysis unit undereffective hydrolysis conditions to produce sugars from thecellulose-rich solids and from the hemicellulose oligomers;

(f) fermenting the sugars to produce ethanol in dilute solution; and

(g) concentrating the dilute solution to produce an ethanol product.

In some variations, a process for producing fermentable sugars fromcellulosic biomass comprises:

(a) providing a feedstock comprising cellulosic biomass;

(b) digesting the feedstock with a reaction solution including steamand/or hot water in a digestor under effective reaction conditions toproduce a digested stream containing cellulose-rich solids,hemicellulose oligomers, and lignin;

(c) reducing pressure of the digested stream;

(d) introducing the digested stream to an enzymatic hydrolysis unitunder effective hydrolysis conditions to produce a liquid phasecomprising sugars from the cellulose-rich solids and optionally from thehemicellulose oligomers, and a solid phase comprising the cellulose-richsolids;

(e) separating the liquid phase and the solid phase from step (d);

(f) conveying the solid phase through a mechanical refiner, therebygenerating a refined stream with reduced average particle size of thecellulose-rich solids;

(g) recycling the refined stream to the enzymatic hydrolysis unit, toproduce additional sugars from the cellulose-rich solids contained inthe solid phase from step (d); and

(h) recovering or further processing at least some of the sugars and atleast some of the additional sugars as fermentable sugars.

Other variations provide a process for producing fermentable sugars fromcellulosic biomass, the process comprising:

(a) providing a feedstock comprising cellulosic biomass;

(b) digesting the feedstock with a reaction solution including steamand/or hot water in a digestor under effective reaction conditions toproduce a digested stream containing cellulose-rich solids,hemicellulose oligomers, and lignin;

(c) reducing pressure of the digested stream;

(d) introducing the digested stream to a first enzymatic hydrolysis unitunder effective hydrolysis conditions to produce a liquid phasecomprising sugars from the cellulose-rich solids and optionally from thehemicellulose oligomers, and a solid phase comprising the cellulose-richsolids;

(e) separating the liquid phase and the solid phase from step (d);

(f) conveying the solid phase through a mechanical refiner, therebygenerating a refined stream with reduced average particle size of thecellulose-rich solids;

(g) recycling the refined stream to a second enzymatic hydrolysis unit,to produce additional sugars from the cellulose-rich solids contained inthe solid phase from step (d); and

(h) recovering or further processing at least some of the sugars and/orthe additional sugars as fermentable sugars.

Other variations provide a process for producing a fermentation productfrom cellulosic biomass, the process comprising:

(a) providing a feedstock comprising cellulosic biomass;

(b) digesting the feedstock with a reaction solution including steamand/or hot water in a digestor under effective reaction conditions toproduce a digested stream containing cellulose-rich solids,hemicellulose oligomers, and lignin;

(c) optionally exploding the digested stream, thereby generating anexploded stream with reduced average particle size of the cellulose-richsolids;

(d) introducing the digested stream and/or (if step (c) is conducted)the exploded stream to an enzymatic hydrolysis unit under effectivehydrolysis conditions to produce a sugar-containing hydrolysate;

(e) evaporating the hydrolysate using a multiple-effect evaporator or amechanical vapor compression evaporator, to produce a concentratedhydrolysate;

(f) fermenting the concentrated hydrolysate to produce a dilutefermentation product; and

(g) concentrating the dilute fermentation product to produce aconcentrated fermentation product.

Some variations provide a process for producing fermentable sugars fromcellulosic biomass, the process comprising:

(a) providing a feedstock comprising cellulosic biomass;

(b) digesting the feedstock with a reaction solution including steamand/or hot water in a digestor under effective reaction conditions toproduce a digested stream containing cellulose-rich solids,hemicellulose oligomers, and lignin;

(c) optionally conveying the digested stream through a mechanicalrefiner, thereby generating a refined stream with reduced averageparticle size of the cellulose-rich solids;

(d) introducing the digested stream and/or (if step (c) is conducted)the refined stream to an enzymatic hydrolysis unit under effectivehydrolysis conditions to produce a sugar-containing hydrolysate;

(e) optionally evaporating the hydrolysate using a multiple-effectevaporator or a mechanical vapor compression evaporator, to produce aconcentrated hydrolysate;

(f) fermenting the hydrolysate to produce a dilute fermentation product;and

(g) concentrating the dilute fermentation product to produce aconcentrated fermentation product.

Other variations provide a process for producing a fermentation productfrom cellulosic biomass, the process comprising:

(a) providing a feedstock comprising cellulosic biomass;

(b) digesting the feedstock with a reaction solution including steamand/or hot water in a digestor under effective reaction conditions toproduce a digested stream containing cellulose-rich solids,hemicellulose oligomers, and lignin;

(c) optionally exploding the digested stream, thereby generating anexploded stream with reduced average particle size of the cellulose-richsolids;

(d) introducing the digested stream and/or (if step (c) is conducted)the exploded stream to an enzymatic hydrolysis unit under effectivehydrolysis conditions to produce a sugar-containing hydrolysate;

(e) evaporating the hydrolysate using a multiple-effect evaporator or amechanical vapor compression evaporator, to produce a concentratedhydrolysate;

(f) fermenting the concentrated hydrolysate to produce a dilutefermentation product; and

(g) concentrating the dilute fermentation product to produce aconcentrated fermentation product.

Other variations provide a process for producing a fermentation productfrom cellulosic biomass, the process comprising:

(a) providing a feedstock comprising cellulosic biomass;

(b) digesting the feedstock with a reaction solution including steamand/or hot water in a digestor under effective reaction conditions toproduce a digested stream containing cellulose-rich solids,hemicellulose oligomers, and lignin;

(c) optionally conveying at least a portion of the digested streamthrough a first mechanical refiner in a blow line;

(d) optionally conveying at least a portion of the digested streamthrough a second mechanical refiner following pressure reduction of thedigested stream;

(e) introducing the digested stream and/or (if step (c) and/or step (d)is conducted) a mechanically treated derivative thereof, to an enzymaticliquefaction unit under effective liquefaction conditions to produce afirst intermediate stream;

(f) optionally conveying at least a portion of the first intermediatestream through a third mechanical refiner;

(g) introducing the first intermediate stream and/or (if step (f) isconducted) a mechanically treated derivative thereof, to a firstenzymatic hydrolysis unit under effective hydrolysis conditions toproduce a second intermediate stream;

(h) optionally conveying at least a portion of the second intermediatestream through a fourth mechanical refiner;

(i) introducing the second intermediate stream and/or (if step (h) isconducted) a mechanically treated derivative thereof, to a secondenzymatic hydrolysis unit under effective hydrolysis conditions toproduce a concentrated hydrolysate;

(j) fermenting the concentrated hydrolysate to produce a dilutefermentation product; and

(k) concentrating the dilute fermentation product to produce aconcentrated fermentation product.

The process may include no refiner, or only the first mechanicalrefiner, or only the second mechanical refiner, or only the thirdmechanical refiner, or only the fourth mechanical refiner, or anycombination thereof (e.g., any two of such refiners, or any three ofsuch refiners, or all four of such refiners).

Some variations provide a process for producing fermentable sugars fromcellulosic biomass, the process comprising:

(a) providing a feedstock comprising cellulosic biomass;

(b) digesting the feedstock with a reaction solution including steamand/or hot water in a digestor under effective reaction conditions toproduce a digested stream containing cellulose-rich solids,hemicellulose oligomers, and lignin;

(c) optionally conveying the digested stream through a mechanicalrefiner, thereby generating a refined stream with reduced averageparticle size of the cellulose-rich solids;

(d) introducing the digested stream and/or (if step (c) is conducted)the refined stream to an enzymatic hydrolysis unit under effectivehydrolysis conditions to produce a sugar-containing hydrolysate;

(e) evaporating the hydrolysate using a multiple-effect evaporator or amechanical vapor compression evaporator, to produce a concentratedhydrolysate;

(f) fermenting the concentrated hydrolysate to produce a dilutefermentation product; and

(g) concentrating the dilute fermentation product to produce aconcentrated fermentation product.

Other variations of the invention provide a process for producingfermentable sugars from cellulosic biomass, the process comprising:

(a) providing a feedstock comprising cellulosic biomass;

(b) digesting the feedstock with a reaction solution including steamand/or hot water in a digestor under effective reaction conditions toproduce a digested stream containing cellulose-rich solids,hemicellulose oligomers, and lignin;

(c) conveying the digested stream through a mechanical refiner, therebygenerating a refined stream with reduced average particle size of thecellulose-rich solids;

(d) introducing enzymes to the mechanical refiner and maintainingeffective hydrolysis conditions to produce sugars from thecellulose-rich solids and optionally from the hemicellulose oligomers,simultaneously with step (c);

(e) evaporating water from the hydrolysate from step (d); and

(f) recovering or further processing at least some of the sugars asfermentable sugars.

Some variations provide a process for producing fermentable sugars fromcellulosic biomass, the process comprising:

(a) providing a feedstock comprising cellulosic biomass;

(b) digesting the feedstock with a reaction solution including steamand/or hot water in a digestor under effective reaction conditions toproduce a digested stream containing cellulose-rich solids,hemicellulose oligomers, and lignin;

(c) conveying the digested stream through a mechanical refiner, therebygenerating a refined stream with reduced average particle size of thecellulose-rich solids;

(d) introducing the refined stream to an acid hydrolysis unit undereffective hydrolysis conditions to produce sugars from thecellulose-rich solids and optionally from the hemicellulose oligomers;

(e) separating a vapor from the refined stream before, during, or afterstep (d); and

(f) recovering or further processing at least some of the sugars asfermentable sugars.

In some embodiments, the reaction solution comprises or consistsessentially of steam in saturated, superheated, or supersaturated form.In these or other embodiments, the reaction solution comprises orconsists essentially of pressurized liquid hot water.

In certain embodiments, a combination of steam and liquid hot water isemployed. For example, a pre-steaming step may be employed prior to thedigestor, and then liquid hot water may be introduced to the digestoralong with pre-steamed biomass. Depending on the temperature andpressure, the steam may partially or completely condense, or the liquidhot water may partially or completely enter the vapor phase, in thedigestor head space and/or within open space between cellulose fibers,for example.

The reaction solution optionally includes an acid catalyst, to assist inextraction of hemicelluloses from the starting material, and possibly tocatalyze some hydrolysis. In some embodiments, the acid is asulfur-containing acid (e.g., sulfur dioxide). In some embodiments, theacid is acetic acid, which may be recovered from the digested stream(i.e., from downstream operations). Additives may be present in thereaction solution, such as acid or base catalysts, or other compoundspresent in recycled streams.

Many types of digestors are possible. The digestor may be horizontal,vertical, or inclined. The digestor may or may not have any internalagitator or means for agitation. The digestor may be fixed in place, orbe allowed to rotate (e.g., about its axial or radial dimensions). Thedigestor may be operated in upflow or downflow mode, relative to thesolids or the solid-liquid mixture. When there is excess liquid, thedigestor may be operated either cocurrently or countercurrently (solidflow versus liquid flow). The digestor may be operated continuously,semi-continuously, in batch, or some combination or hybrid thereof. Theflow pattern in the digestor may be plug flow, well-mixed, or any otherflow pattern. The digestor may be heated internally or externally, suchas by steam, hot oil, etc. Generally, the principles of chemical-reactorengineering may be applied to digestor design and operation.

In certain preferred embodiments of the invention, the digestor is avertical digestor. In some embodiments, the digestor is not or does notinclude a horizontal digestor (e.g., Pandia-type). Although the priorart tends to teach away from a vertical digestor for processing annualfibers (agricultural residues), it has been discovered that asingle-stage pretreatment in a vertical digestor works surprisingly wellfor steam or hot-water extraction of agricultural residues prior toenzymatic hydrolysis.

As intended herein, a “vertical digestor” can include non-verticalancillary equipment, including feeding and discharge equipment. Forexample, a horizontal or inclined inlet (e.g., plug-screw feeder) orhorizontal or inclined outlet (e.g., plug-screw discharger), ahorizontal or inclined pre-impregnator, a horizontal or inclined blowline, and so on may be included in the process when a vertical digestoris utilized. Also, a vertical digestor may be substantially vertical butmay contain sections or zones that are not strictly vertical, and maycontain side-streams (inlet or outlet), internal recycle streams, and soon that may be construed as non-vertical. In some embodiments, avertical digestor has a varying diameter along its length (height).

In certain preferred embodiments of the invention, the digestor is asingle-stage digestor. Here “single stage” means that biomass isextracted with an extraction solution (e.g., liquid hot water with anoptional acid such as acetic acid) at reaction temperature and pressure,to solubilize hemicelluloses and lignin, with no intermediate separationprior to entering a mechanical refiner, blow line, or blow valve. Thehemicelluloses are not separated and the cellulose-rich solids are notseparately processed prior to enzymatic hydrolysis. Following thedigestor and optional blow-line refiner, and after the pressure isreleased to reach atmospheric pressure, in some embodiments, thehemicelluloses may be washed from the solids and separately processed tohydrolyze hemicelluloses to monomers and/or to separately fermenthemicellulose sugars to ethanol. In some embodiments, there is nointermediate separation: all extracted/digested contents—both the solidand liquid phases—are sent to enzymatic hydrolysis to produce glucoseand other monomer sugars such as xylose.

Some specific embodiments of the invention employ a single-stagevertical digestor configured to continuously pretreat incoming biomasswith liquid hot water, followed by blow-line refining of the entirepretreated material, and then followed by enzymatic hydrolysis of theentire refined material.

The mechanical refiner may be selected from the group consisting of ahot-blow refiner, a hot-stock refiner, a blow-line refiner, a diskrefiner, a conical refiner, a cylindrical refiner, an in-linedefibrator, a homogenizer, and combinations thereof (noting that theseindustry terms are not mutually exclusive to each other). In certainembodiments, the mechanical refiner is a blow-line refiner. Othermechanical refiners may be employed, and chemical refining aids (e.g.,fatty acids) may be introduced, such as to adjust viscosity, density,lubricity, etc.

Mechanically treating (refining) may employ one or more known techniquessuch as, but by no means limited to, milling, grinding, beating,sonicating, or any other means to reduce cellulose particle size. Suchrefiners are well-known in the industry and include, without limitation,Valley beaters, single disk refiners, double disk refiners, conicalrefiners, including both wide angle and narrow angle, cylindricalrefiners, homogenizers, microfluidizers, and other similar milling orgrinding apparatus. See, for example, Smook, Handbook for Pulp & PaperTechnologists, Tappi Press, 1992.

A pressurized refiner may operate at the same pressure as the digestor,or at a different pressure. In some embodiments, both the digestor andthe refiner operate in a pressure range corresponding to equilibriumsteam saturation temperatures from about 170° C. to about 210° C., suchas about 180° C. to about 200° C. In some embodiments, a pressurizedrefiner is fed by a screw between the digestor and the refiner.

In principle, the pressure in the refiner could be higher than thedigestor pressure, due to mechanical energy input. For example, ahigh-pressure screw feeder could be utilized to increase refiningpressure, if desired. Also, it will be recognized that localizedpressures (force divided by area) may be higher than the vapor pressure,due to the presence of mechanical surface force (e.g., plates) impactingthe solid material or slurry.

A blow tank may be situated downstream of the mechanical refiner, sothat the mechanical refiner operates under pressure. The pressure of themechanical refiner may be the same as the digestor pressure, or it maybe different. In some embodiments, the mechanical refiner is operated ata refining pressure selected from about 30 psig (2.07 bar, noting that“bar” herein refers to gauge pressure) to about 300 psig (20.7 bar),such as about 50 psig (3.45 bar) to about 150 psig (10.3 bar).

A blow tank may be situated upstream of the mechanical refiner, so thatthe mechanical refiner operates under reduced pressure or atmosphericpressure. In some embodiments, the mechanical refiner is operated arefining pressure of less than about 50 psig, less than about 30 psig,or at or about atmospheric pressure.

Note that “blow tank” should be broadly construed to include not only atank but any other apparatus or equipment capable of allowing a pressurereduction in the process stream. Thus a blow tank may be a tank, vessel,section of pipe, valve, separation device, or other unit.

In some embodiments, following a digestor to remove hemicellulose, anintermediate blow is performed to, for example, about 40 psig. Thematerial is sent to a blow-line refiner, and then to a final blow toatmospheric pressure, for example. In some embodiments, a cold blowdischarger is utilized to feed a pressurized refiner. In someembodiments, a transfer conveyor is utilized to feed a pressurizedrefiner.

The refining may be conducted at a wide range of solids concentrations(consistency), including from about 2% to about 50% consistency, such asabout 4%, 6%, 8%, 10%, 15%, 20%, 30%, 35%, or 40% consistency.

A pressurized refiner may operate at the same pressure as the digestor,or at a different pressure. In some embodiments, both the digestor andthe refiner operate in a pressure range corresponding to equilibriumsteam saturation temperatures from about 170° C. to about 210° C., suchas about 180° C. to about 200° C. In some embodiments, a pressurizedrefiner is fed by a screw between the digestor and the refiner.

In certain embodiments of the invention, a first blow tank is situatedupstream of the mechanical refiner and a second blow tank is situateddownstream of the mechanical refiner. In this scenario, the pressure isreduced somewhat between the digestor and the refiner, which operatesabove atmospheric pressure. Following the refining, the pressure isreleased in the second blow tank. In some embodiments, the mechanicalrefiner is operated at a refining pressure selected from about 10 psigto about 150 psig, such as about 20 psig to about 100 psig, or about 30psig to about 50 psig.

In some embodiments, the vapor is separated from a blow tank, and heatis recovered from at least some of the vapor. At least some of the vapormay be compressed and returned to the digestor. Some of the vapor may bepurged from the process.

In some embodiments, heat is recovered from at least some of the vapor,using the principles of heat integration. At least some of the vapor maybe compressed and returned to the digestor. Some of the vapor may bepurged from the process.

In certain embodiments, the reduction of pressure that occurs across ablow valve causes, or assists, fiber expansion or fiber explosion. Fiberexpansion or explosion is a type of physical action that can occur,reducing particle size or surface area of the cellulose phase, andenhancing the enzymatic digestibility of the pretreated cellulose.Certain embodiments employ a blow valve (or multiple blow valves) toreplace a mechanical refiner or to augment the refining that resultsfrom a mechanical refiner, disposed either before or after such blowvalve. Some embodiments combine a mechanical refiner and blow value intoa single apparatus that simultaneously refines the cellulose-rich solidswhile blowing the material to a reduced pressure.

In some embodiments, enzymes introduced or present in the enzymatichydrolysis unit may include not only cellulases but also hemicellulases.In certain embodiments, enzymes introduced or present in the enzymatichydrolysis unit include endoglucanases and exoglucanases.

Enzymatic hydrolysis may be conducted at a solids concentration fromabout 5 wt % to about 25 wt %, such as about 10 wt %, 12 wt %, 15 wt %,18 wt %, 20 wt %, or 22 wt %.

The enzymatic hydrolysis unit may include a single stage configured forcellulose liquefaction and saccharification, wherein the single stageincludes one or more tanks or vessels. Alternatively, the enzymatichydrolysis unit may include two stages configured for celluloseliquefaction followed by saccharification, wherein each stage includesone or more tanks or vessels.

Enzymes introduced or present in the enzymatic hydrolysis unit mayinclude cellulases and hemicellulases. In some embodiments, enzymesintroduced or present in the enzymatic hydrolysis unit includeendoglucanases and exoglucanases.

Some embodiments employ two or more enzymatic hydrolysis units. Thefirst enzymatic hydrolysis unit may include a single stage configuredfor cellulose liquefaction and saccharification, wherein the singlestage includes one or more tanks or vessels. Alternatively, the firstenzymatic hydrolysis unit may include two stages configured forcellulose liquefaction followed by saccharification, wherein each stageincludes one or more tanks or vessels.

The second enzymatic hydrolysis unit may include a single stageconfigured for cellulose liquefaction and saccharification, wherein thesingle stage includes one or more tanks or vessels. Alternatively, thesecond enzymatic hydrolysis unit may include two stages configured forcellulose liquefaction followed by saccharification, wherein each stageincludes one or more tanks or vessels. In certain embodiments, theprocess further comprises recycling at least some material treated inthe second enzymatic hydrolysis unit, for solid/liquid separation, forexample.

Enzymes introduced or present in the enzymatic hydrolysis unit mayinclude cellulases and hemicellulases. In some embodiments, enzymesintroduced or present in the enzymatic hydrolysis unit includeendoglucanases and exoglucanases.

The hydrolysis reactor may be configured in one or more stages orvessels. In some embodiments, a hydrolysis reactor is a system of two,three, or more physical vessels which are configured to carry outliquefaction or hydrolysis of sugar oligomers. For example, in certainembodiments, a liquefaction tank is followed by a hydrolysis tank, whichis then followed by another tank for extended hydrolysis. Enzymes may beadded to any one or more of these vessels, and enzyme recycling may beemployed.

In other embodiments, a single physical hydrolysis reactor is utilized,which reactor contains a plurality of zones, such as a liquefactionzone, a first hydrolysis zone, and a second hydrolysis zone. The zonesmay be stationary or moving, and the reactor may be a continuousplug-flow reactor, a continuous stirred reactor, a batch reactor, asemi-batch reactor, or any combination of these, including arbitraryflow patterns of solid and liquid phases.

A mechanical refiner may be included before liquefaction, between theliquefaction tank and hydrolysis tank, and/or between the hydrolysistank and the extended hydrolysis tank. Alternatively or additionally, amechanical refiner may be included elsewhere in the process. Enzymes maybe introduced directly into any of the refiners, if desired.

In some embodiments, enzymes are introduced directly to the mechanicalrefiner. In these or other embodiments, the enzymes are introduced tothe digested stream, upstream of the mechanical refiner. The enzymes mayinclude cellulases (e.g., endoglucanases and exoglucanases) andhemicellulases.

The effective hydrolysis conditions may include a maximum temperature of75° C. or less, preferably 65° C. or less, within the mechanicalrefiner. In some embodiments, the effective hydrolysis conditionsinclude a hydrolysis temperature of about 30° C., 40° C., 50° C., 60°C., or 70° C. within the mechanical refiner. These are averagetemperatures within the refining zone. Local hot spots may be presentwithin the refiner, such as in regions of high-shear, high-frictioncontact between cellulose-rich solids and metal plates.

In some embodiments, a hydrolysis reactor or a refiner is configured tocause at least some liquefaction as a result of enzymatic action on thecellulose-rich solids. “Liquefaction” means partial hydrolysis ofcellulose to form glucose oligomers (i.e. glucan) that dissolve intosolution, but not total hydrolysis of cellulose to glucose monomers(saccharification). Various fractions of cellulose may be hydrolyzedduring liquefaction. In some embodiments, the fraction of cellulosehydrolyzed may be from about 5% to about 90%, such as about 10% to about75% (e.g. about 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%,or 70%). In certain embodiments, there is no separate liquefaction tankor reactor; liquefaction and hydrolysis occur in the same vessel (e.g.,refiner or hydrolysis reactor).

A “liquefaction-focused blend of enzymes” means a mixture of enzymesthat includes at least one enzyme capable of hydrolyzing cellulose toform soluble oligomers. In some embodiments, a liquefaction-focusedblend of enzymes includes both endoglucanases and exoglucanases.Endoglucanases are cellulases that attack low-crystallinity regions inthe cellulose fibers by endoaction, creating free chain-ends.Exoglucanases or cellobiohydrolases are cellulases that hydrolyze the1,4-glycocidyl linkages in cellobiose.

Various cellulase enzymes may be utilized in the liquefaction-focusedblend of enzymes, such as one or more enzymes recited in Verardi et al.,“Hydrolysis of Lignocellulosic Biomass: Current Status of Processes andTechnologies and Future Perspectives,” Bioethanol, Prof Marco AurelioPinheiro Lima (Ed.), ISBN: 978-953-51-0008-9, InTech (2012), which ishereby incorporated by reference.

Some embodiments employ thermotolerant enzymes obtained fromthermophilic microrganisms. The thermophilic microrganisms can begrouped in thermophiles (growth up to 60° C.), extreme thermophiles(65-80° C.) and hyperthermophiles (85-110° C.). The unique stability ofthe enzymes produced by these microrganisms at elevated temperatures,extreme pH and high pressure (up to 1000 bar) makes them valuable forprocesses at harsh conditions. Also, thermophilic enzymes have anincreased resistance to many denaturing conditions such as the use ofdetergents which can be an efficient means to obviate the irreversibleadsorption of cellulases on the substrates. Furthermore, the utilizationof high operation temperatures, which cause a decrease in viscosity andan increase in the diffusion coefficients of substrates, have asignificant influence on the cellulose solubilization. Most thermophiliccellulases do not show inhibition at high level of reaction products(e.g. cellobiose and glucose). As consequence, higher reaction rates andhigher process yields are expected. The high process temperature alsoreduces contamination. See Table 6, “Thermostable cellulases” in Verardiet al., cited above, for exemplary thermotolerant enzymes that may beused in the liquefaction-focused blend of enzymes, or in otherembodiments herein

In some embodiments, an enzyme is selected such that at a hightemperature, the enzyme is able to catalyze liquefaction (partialhydrolysis) but not saccharification (total hydrolysis). When thetemperature is reduced, the same enzyme is able to catalyzesaccharification to produce glucose.

When the hydrolysis process employs enzymes, these enzymes willtypically contain cellulases and hemicellulases. The cellulases here mayinclude β-glucosidases that convert cellooligosaccharides anddisaccharide cellobiose into glucose. There are a number of enzymes thatcan attack hemicelluloses, such as glucoronide, acetylesterase,xylanase, β-xylosidase, galactomannase and glucomannase. Exemplary acidcatalysts include sulfuric acid, sulfur dioxide, hydrochloric acid,phosphoric acid, and nitric acid.

In certain embodiments of the invention, a self-cleaning filter isconfigured downstream of a hydrolysis tank to remove cellulose fiberstrands prior to sending the hydrolysate to a fermentor or other unit(e.g., another hydrolysis vessel for extended hydrolysis of solublematerial). The self-cleaning filter continuously rejects solids(including cellulose fiber strands) that may be recycled back to thefirst hydrolysis vessel. For example, the cellulose fiber strands may berecycled to a biomass cooler that feeds a viscosity-reduction tank atthe beginning of hydrolysis.

Many fluid streams contain particulate matter, and it is often desirableto separate this particulate matter from the fluid stream. If notseparated, the particulate matter may degrade product quality,efficiency, reduce performance, or cause severe damage to componentswithin the system. Many types of filters have been designed for thepurpose of removing particulate matter from fluid streams. Such filtershave typically included a filter element designed to screen theparticulate material. However, the particulate material often becomesentrapped in the filter element. As the quantity of particulatematerial, often referred to as filter cake, collects on the filterelement, the pressure drop that occurs across the filter elementincreases. A pressure drop across the filter element of sufficientmagnitude can significantly reduce fluid flow at which point the filterelement must be periodically cleaned, or replaced with a new filter.Often, this is done manually by removing the filter element and cleaningthe filter before reinstalling it back in the system. To minimize manualoperations, filters have been designed to accomplish continuousself-cleaning.

As intended herein, a “self-cleaning filter” should be construed broadlyto refer to self-cleaning filtration devices, self-cleaning decanters,self-cleaning screens, self-cleaning centrifuges, self-cleaningcyclones, self-cleaning rotary drums, self-cleaning extruders, or otherself-cleaning separation devices.

Some self-cleaning filters use back pulsing to dislodge materials orblades to scrape off caked particulate. Some self-cleaning filters arecleaned with sprayed fluids, such as water or air to remove theparticulates. Some self-cleaning filters utilize high pressures orforces to dislodge caked particulate from the filter. Some self-cleaningfilters employ a moving (e.g., rotating) filter design whereinparticulates are continuously filtered and removed due to centrifugalforce or other forces. Many self-cleaning filters are availablecommercially.

Also see, for example, U.S. Pat. No. 4,552,655, issued Nov. 12, 1985 andU.S. Pat. No. 8,529,661, issued Sep. 10, 2013, which are herebyincorporated by reference as prior art for self-cleaning filters.

As intended herein, “cellulose fiber strands” generally refer torelatively large, non-soluble cellulose-containing particles in the formof individual fibers or bundles of fibers. Cellulose fiber strands,without limitation, may have lengths or effective lengths in the rangeof about 0.1 mm to about 10 mm, such as about 0.5 mm to about 5 mm. Somefiber strand bundles may have very large length or particle size, suchas about 10 mm or more. The principles of the invention may be appliedto smaller cellulose particles, with length or particle size less than0.1 mm, as long as the particles can be captured by a self-cleaningfilter.

In some embodiments, the composition of some cellulose fiber strands maybe similar to the composition of the starting biomass material, such aswhen large particles were not effectively pretreated in the digestor.

In some embodiments, a self-cleaning filter is configured downstream ofan enzymatic hydrolysis unit to remove cellulosic fiber strands. Theself-cleaning filter is preferably operated continuously. The cellulosicfiber strands may be recycled back to one or more of the one or moreenzymatic hydrolysis units, for further cellulose hydrolysis.

In some embodiments of the invention, a self-cleaning filter isconfigured downstream of the enzymatic liquefaction unit to removecellulosic fiber strands. In these or other embodiments, a self-cleaningfilter is configured downstream of the first enzymatic hydrolysis unitto remove cellulosic fiber strands. In these or other embodiments, aself-cleaning filter is configured downstream of the second enzymatichydrolysis unit to remove cellulosic fiber strands.

At least a portion of the cellulosic fiber strands may be recycled backto the enzymatic liquefaction unit or to vessel or heat exchanger thatfeeds into the enzymatic liquefaction unit. Alternatively, oradditionally, at least a portion of the cellulosic fiber strands arerecycled back to the first enzymatic hydrolysis unit or to vessel orheat exchanger that feeds into the first enzymatic hydrolysis unit.Alternatively, or additionally, at least a portion of the cellulosicfiber strands are recycled back to the digestor and/or to one of themechanical refiners.

Generally speaking, the enzymatic hydrolysis that follows thehydrothermal-mechanical process should be optimized for the biomasstype, the capital cost of tanks versus solids content, energyintegration with the rest of the plant, and enzyme cost versus sugaryield. For each commercial implementation, one skilled in the art maycarry out a design of experiments in cooperation with an enzymesupplier, or in conjunction with on-site enzyme production. In someembodiments, a process disclosed herein is retrofitted to an existingdigestor, and existing refiner, an existing hydrolysis reactor, and/oran existing fermentation system. Such a retrofit needs to adapt to siteconstraints.

The process may further include removal of one or more fermentationinhibitors by stripping. This stripping may be conducted following step(e), i.e. treating the hydrolyzed cellulose stream, prior tofermentation. Alternatively, or additionally, the stripping may beconducted on a stream following digestion, such as in the blow line, oras part of an acetic acid recycle system.

The process may further include a step of fermenting the fermentablesugars to a fermentation product. Typically the process will furtherinclude concentration and purification of the fermentation product. Thefermentation product may be selected from ethanol, n-butanol,1,4-butanediol, succinic acid, lactic acid, or combinations thereof, forexample. The lignin may be combusted for energy production.

Some embodiments further include removing a solid stream containinglignin following prior to fermentation of the fermentable sugars. Inthese or other embodiments, the process may further include removing asolid stream containing lignin following fermentation of the fermentablesugars. The lignin may be combusted or used for other purposes.

Some variations described herein are premised on the design of processoptions to increase the yield of ethanol production (or otherfermentation product). Some process configurations include sendingdigested pulp, after a hot blow but before any mechanical refining, tocontinuous enzymatic hydrolysis. The enzymatic hydrolysis may beconfigured in one step (liquefaction and saccharification in one vessel)or two steps (tanks) in series. The different vessels may bedesigned/operated as continuous stirred tank reactors. The material(liquid and solid) from the enzymatic hydrolysis may undergo asolid/liquid separation, wherein the liquid phase containing C₅ and C₆sugars is sent to fermentation. The solid phase may be sent to anatmospheric pulp refiner wherein further deconstruction of thenon-hydrolyzed fiber (solid phase) is achieved by adjusting the refinerpower load and physical parameters (e.g., dimensions of gaps orgrooves). Next, the refined fiber is sent to another enzymatichydrolysis unit or is recycled back to the primary hydrolysis unit.These embodiments may increase enzymatic hydrolysis yield by recyclingmore deconstructed fiber, and/or increase fiber digestibility tofermentation microorganisms which translates into higher ethanol yield.Less solids sent to fermentation translates to higher fermentationyield. A cleaner fermentation beer which will produce less fouling ofthe beer column.

In some variations, a process for producing fermentable sugars fromcellulosic biomass comprises:

(a) providing a feedstock comprising cellulosic biomass;

(b) digesting the feedstock with a reaction solution including steamand/or hot water in a digestor under effective reaction conditions toproduce a digested stream containing cellulose-rich solids,hemicellulose oligomers, and lignin;

(c) reducing pressure of the digested stream;

(d) introducing the digested stream to an enzymatic hydrolysis unitunder effective hydrolysis conditions to produce a liquid phasecomprising sugars from the cellulose-rich solids and optionally from thehemicellulose oligomers, and a solid phase comprising the cellulose-richsolids;

(e) separating the liquid phase and the solid phase from step (d);

(f) conveying the solid phase through a mechanical refiner, therebygenerating a refined stream with reduced average particle size of thecellulose-rich solids;

(g) recycling the refined stream to the enzymatic hydrolysis unit, toproduce additional sugars from the cellulose-rich solids contained inthe solid phase from step (d); and

(h) recovering or further processing at least some of the sugars and atleast some of the additional sugars as fermentable sugars.

Other variations provide a process for producing fermentable sugars fromcellulosic biomass, the process comprising:

(a) providing a feedstock comprising cellulosic biomass;

(b) digesting the feedstock with a reaction solution including steamand/or hot water in a digestor under effective reaction conditions toproduce a digested stream containing cellulose-rich solids,hemicellulose oligomers, and lignin;

(c) reducing pressure of the digested stream;

(d) introducing the digested stream to a first enzymatic hydrolysis unitunder effective hydrolysis conditions to produce a liquid phasecomprising sugars from the cellulose-rich solids and optionally from thehemicellulose oligomers, and a solid phase comprising the cellulose-richsolids;

(e) separating the liquid phase and the solid phase from step (d);

(f) conveying the solid phase through a mechanical refiner, therebygenerating a refined stream with reduced average particle size of thecellulose-rich solids;

(g) recycling the refined stream to a second enzymatic hydrolysis unit,to produce additional sugars from the cellulose-rich solids contained inthe solid phase from step (d); and

(h) recovering or further processing at least some of the sugars and/orthe additional sugars as fermentable sugars.

Some variations provide a process for producing fermentable sugars fromcellulosic biomass, the process comprising:

(a) providing a feedstock comprising cellulosic biomass;

(b) digesting the feedstock with a reaction solution including steamand/or hot water in a digestor under effective reaction conditions toproduce a digested stream containing cellulose-rich solids,hemicellulose oligomers, and lignin;

(c) optionally conveying the digested stream through a mechanicalrefiner, thereby generating a refined stream with reduced averageparticle size of the cellulose-rich solids;

(d) introducing the digested stream and/or (if step (c) is conducted)the refined stream to an enzymatic hydrolysis unit under effectivehydrolysis conditions to produce a sugar-containing hydrolysate;

(e) evaporating the hydrolysate using a multiple-effect evaporator or amechanical vapor compression evaporator, to produce a concentratedhydrolysate;

(f) fermenting the concentrated hydrolysate to produce a dilutefermentation product; and

(g) concentrating the dilute fermentation product to produce aconcentrated fermentation product.

Step (d) may be conducted at a solids concentration from about 5 wt % toabout 25 wt %, such as about 10 wt %, 15 wt %, or 20 wt %.

Step (g) may utilize distillation, which generates a distillationbottoms stream. In some embodiments, the distillation bottoms stream isevaporated in a distillation bottoms evaporator that is integrated withstep (e) in a multiple-effect evaporator train. The distillation bottomsevaporator may provide lignin-rich combustion fuel.

Suspended solids (lignin or other solids) may be removed prior to step(e). In some embodiments, suspended solids are during or after step (e)and prior to the distillation bottoms evaporator.

The concentrated fermentation product may be selected from ethanol,n-butanol, isobutanol, 1,4-butanediol, succinic acid, lactic acid, orcombinations thereof, for example. In certain embodiments, theconcentrated fermentation product is ethanol.

In some embodiments, the process includes washing the cellulose-richsolids using an aqueous wash solution, to produce a wash filtrate; andoptionally combining at least some of the wash filtrate with the extractliquor. In some of these embodiments, the process further includespressing the cellulose-rich solids to produce the washed cellulose-richsolids and a press filtrate; and optionally combining at least some ofthe press filtrate with the extract liquor.

The process may include countercurrent washing, such as in two, three,four, or more washing stages. The separation/washing may be combinedwith the application of enzymes, in various ways.

Two hydrolysis catalysts may be utilized in series. In some embodiments,a first hydrolysis catalyst includes cellulases. In some embodiments, asecond hydrolysis catalyst includes hemicellulases. In otherembodiments, the first hydrolysis catalyst and the second hydrolysiscatalyst are acid catalysts, base catalysts, ionic liquids, solidcatalysts, or other effective materials. The first hydrolysis catalystmay be the same as, or different than, the second hydrolysis catalyst.

In some embodiments, the glucose is recovered in a separate stream fromthe hemicellulose monomers. In other embodiments, the glucose and thehemicellulose monomers are recovered in the same stream. The process mayinclude fermentation of the glucose and/or the fermentable hemicellulosesugars to a fermentation product.

In some embodiments, the process starts as biomass is received orreduced to a desired particle size. In a first step of the process, thebiomass is fed (e.g., from a feed bin) to a pressurized extractionvessel operating continuously or in batch mode. The biomass may first besteamed or water-washed to remove dirt and entrained air. The biomass isimmersed with aqueous liquor or saturated vapor and heated to atemperature between about 100° C. to about 250° C., for example 150° C.,160° C., 170° C., 180° C., 190° C., 200° C., or 210° C. Preferably, thebiomass is heated to about 180° C. to 210° C.

The pressure in the pressurized vessel may be adjusted to maintain theaqueous liquor as a liquid, a vapor, or a combination thereof. Exemplarypressures are about 1 bar to about 30 bar, such as about 3 bar, 5 bar,10 bar, or 15 bar.

The solid-phase residence time for the digestor (pressurized extractionvessel) may vary from about 2 minutes to about 4 hours, such as about 5minutes to about 1 hour. In certain embodiments, the digestor residencetime is controlled to be about 5 to 15 minutes, such as 5, 6, 7, 8, 9,10, 11, 12, 13, 14 or 15 minutes. The liquid-phase residence time forthe digestor may vary from about 2 minutes to about 4 hours, such asabout 5 minutes to about 1 hour. The vapor-phase residence time for thedigestor may vary from about 1 minute to about 2 hours, for example,such as about 3 minutes to about 30 minutes. The solid-phase,liquid-phase, and vapor-phase residence times may all be about the same,or they may be independently controlled according to reactor-engineeringprinciples (e.g., recycling and internal recirculation strategies).

The aqueous liquor may contain acidifying compounds, such as (but notlimited to) sulfuric acid, sulfurous acid, sulfur dioxide, acetic acid,formic acid, or oxalic acid, or combinations thereof. The dilute acidconcentration (if any) can range from 0.01 wt % to 10 wt % as necessaryto improve solubility of particular minerals, such as potassium, sodium,or silica. Preferably, the acid concentration is selected from about0.01 wt % to 4 wt %, such as 0.1 wt %, 0.5 wt %, or 1 wt %.

A second step may include depressurization of the extracted biomass intoa blow tank or other tank or unit. The vapor can be used for heating theincoming biomass or cooking liquor, directly or indirectly. Thevolatilized organic acids (e.g., acetic acid), which are generated orincluded in the cooking step, may be recycled back to the cooking.

A third step may include mechanically refining the extracted biomass.This step (using, for example, a blow-line refiner) may be done beforeor after depressurization.

Optionally, refined solids may be washed. The washing may beaccomplished with water, recycled condensates, recycled permeate, or acombination thereof. Washing typically removes most of the dissolvedmaterial, including hemicelluloses and minerals. The final consistencyof the dewatered cellulose-rich solids may be increased to 30% or more,preferably to 50% or more, using a mechanical pressing device. Themechanical pressing device may be integrated with the mechanicalrefiner, to accomplish combined refining and washing.

A fourth step may include hydrolyzing the extracted chips with enzymesto convert some of the cellulose to glucose. When enzymes are employedfor the cellulose hydrolysis, the enzymes preferably include cellulaseenzymes. Enzymes may be introduced to the extracted chips along withwater, recycled condensates, recycled permeate, additives to adjust pH,additives to enhance hydrolysis (such as lignosulfonates), orcombinations thereof.

Some or all of the enzymes may be added to the blow line before or atthe blow-line refiner, for example, to assist in enzyme contact withfibers. In some embodiments, at least a portion of enzymes are recycledin a batch or continuous process.

When an acid is employed for the cellulose hydrolysis, the acid may beselected from sulfuric acid, sulfurous acid, sulfur dioxide, formicacid, acetic acid, oxalic acid, or combinations thereof. Acids may beadded to the extracted chips before or after mechanical refining. Insome embodiments, dilute acidic conditions are used at temperaturesbetween about 100° C. and 190° C., for example about 120° C., 130° C.,140° C., 150° C., 160° C., or 170° C., and preferably from 120° C. to150° C. In some embodiments, at least a portion of the acid is recycledin a batch or continuous process.

The acid may be selected from sulfuric acid, sulfurous acid, or sulfurdioxide. Alternatively, or additionally, the acid may include formicacid, acetic acid, or oxalic acid from the cooking liquor or recycledfrom previous hydrolysis.

A fifth step may include conditioning of hydrolysate to remove some ormost of the volatile acids and other fermentation inhibitors. Theevaporation may include flashing or stripping to remove sulfur dioxide,if present, prior to removal of volatile acids. The evaporation step ispreferably performed below the acetic acid dissociation pH of 4.8, andmost preferably a pH selected from about 1 to about 2.5. In someembodiments, additional evaporation steps may be employed. Theseadditional evaporation steps may be conducted at different conditions(e.g., temperature, pressure, and pH) relative to the first evaporationstep.

In some embodiments, some or all of the organic acids evaporated may berecycled, as vapor or condensate, to the first step (cooking step) toassist in the removal of hemicelluloses or minerals from the biomass.This recycle of organic acids, such as acetic acid, may be optimizedalong with process conditions that may vary depending on the amountrecycled, to improve the cooking effectiveness.

A sixth step may include recovering fermentable sugars, which may bestored, transported, or processed. A sixth step may include fermentingthe fermentable sugars to a product, as further discussed below.

A seventh step may include preparing the solid residuals (containinglignin) for combustion. This step may include refining, milling,fluidizing, compacting, and/or pelletizing the dried, extracted biomass.The solid residuals may be fed to a boiler in the form of fine powder,loose fiber, pellets, briquettes, extrudates, or any other suitableform. Using known equipment, solid residuals may be extruded through apressurized chamber to form uniformly sized pellets or briquettes.

In some embodiments, the fermentable sugars are recovered from solution,in concentrated form. In some embodiments, the fermentable sugars arefermented to produce of biochemicals or biofuels such as (but by nomeans limited to) ethanol, 1-butanol, isobutanol, acetic acid, lacticacid, or any other fermentation products. A purified fermentationproduct may be produced by distilling the fermentation product, whichwill also generate a distillation bottoms stream containing residualsolids. A bottoms evaporation stage may be used, to produce residualsolids.

Following fermentation, residual solids (such as distillation bottoms)may be recovered, or burned in solid or slurry form, or recycled to becombined into the biomass pellets. Use of the fermentation residualsolids may require further removal of minerals. Generally, any leftoversolids may be used for burning, after concentration of the distillationbottoms.

Alternatively, or additionally, the process may include recovering theresidual solids as a fermentation co-product in solid, liquid, or slurryform. The fermentation co-product may be used as a fertilizer orfertilizer component, since it will typically be rich in potassium,nitrogen, and/or phosphorous.

In certain embodiments, the process further comprises combining, at a pHof about 4.8 to 10 or higher, a portion of vaporized acetic acid with analkali oxide, alkali hydroxide, alkali carbonate, and/or alkalibicarbonate, wherein the alkali is selected from the group consisting ofpotassium, sodium, magnesium, calcium, and combinations thereof, toconvert the portion of the vaporized acetic acid to an alkaline acetate.The alkaline acetate may be recovered. If desired, purified acetic acidmay be generated from the alkaline acetate.

In some variations, fermentation inhibitors are separated from abiomass-derived hydrolysate, such as by the following steps:

(a) providing a biomass-derived liquid hydrolysate stream comprising afermentation inhibitor;

(b) introducing the liquid hydrolysate stream to a stripping column;

(c) introducing a steam-rich vapor stream to the stripping column tostrip at least a portion of the fermentation inhibitor from the liquidhydrolysate stream;

(d) recovering, from the stripping column, a stripped liquid stream anda stripper vapor output stream, wherein the stripped liquid stream haslower fermentation inhibitor concentration than the liquid hydrolysatestream;

(e) compressing the stripper vapor output stream to generate acompressed vapor stream;

(f) introducing the compressed vapor stream, and a water-rich liquidstream, to an evaporator;

(g) recovering, from the evaporator, an evaporated liquid stream and anevaporator output vapor stream; and

(h) recycling at least a portion of the evaporator output vapor streamto the stripping column as the steam-rich vapor stream, or a portionthereof.

The biomass-derived hydrolysate may be the product of acidic orenzymatic hydrolysis, or it may be the extracted solution from thedigestor, for example. In some embodiments, the fermentation inhibitoris selected from the group consisting of acetic acid, formic acid,formaldehyde, acetaldehyde, lactic acid, furfural,5-hydroxymethylfurfural, furans, uronic acids, phenolic compounds,sulfur-containing compounds, and combinations or derivatives thereof.

In some embodiments, the water-rich liquid stream contains biomasssolids that are concentrated in the evaporator. These biomass solids maybe derived from the same biomass feedstock as is the biomass-derivedliquid hydrolysate, in an integrated process.

Optionally, the fermentation inhibitor is recycled to a previous unitoperation (e.g., digestor or reactor) for generating the biomass-derivedliquid hydrolysate stream, to assist with hydrolysis or pretreatment ofa biomass feedstock or component thereof. For example, acetic acid maybe recycled for this purpose, to aid in removal of hemicelluloses frombiomass and/or in oligomer hydrolysis to monomer sugars.

Some variations provide a process for separating fermentation inhibitorsfrom a biomass-derived hydrolysate, the process comprising:

(a) providing a biomass-derived liquid hydrolysate stream comprising afermentation inhibitor;

(b) introducing the liquid hydrolysate stream to a stripping column;

(c) introducing a steam-rich vapor stream to the stripping column tostrip at least a portion of the fermentation inhibitor from the liquidhydrolysate stream;

(d) recovering, from the stripping column, a stripped liquid stream anda stripper vapor output stream, wherein the stripped liquid stream haslower fermentation inhibitor concentration than the liquid hydrolysatestream;

(e) introducing the stripper vapor output stream, and a water-richliquid stream, to an evaporator;

(f) recovering, from the evaporator, an evaporated liquid stream and anevaporator output vapor stream;

(g) compressing the evaporator output vapor stream to generate acompressed vapor stream; and

(h) recycling at least a portion of the compressed vapor stream to thestripping column as the steam-rich vapor stream, or a portion thereof.

In some embodiments, the evaporator is a boiler, the water-rich liquidstream comprises boiler feed water, and the evaporated liquid streamcomprises boiler condensate.

The process may be continuous, semi-continuous, or batch. Whencontinuous or semi-continuous, the stripping column may be operatedcountercurrently, cocurrently, or a combination thereof.

In certain variations, a process for separating and recovering afermentation inhibitor from a biomass-derived hydrolysate comprises:

(a) providing a biomass-derived liquid hydrolysate stream comprising afermentation inhibitor;

(b) introducing the liquid hydrolysate stream to a stripping column;

(c) introducing a steam-rich vapor stream to the stripping column tostrip at least a portion of the fermentation inhibitor from the liquidhydrolysate stream;

(d) recovering, from the stripping column, a stripped liquid stream anda stripper vapor output stream, wherein the stripped liquid stream haslower fermentation inhibitor concentration than the liquid hydrolysatestream;

(e) introducing the stripper vapor output stream, and a water-richliquid stream, to a rectification column;

(f) recovering, from the rectification column, a rectified liquid streamand a rectification column vapor stream, wherein the rectified liquidstream has higher fermentation inhibitor concentration than the liquidhydrolysate stream; and

(g) recycling at least a portion of the rectification column vaporstream to the stripping column as the steam-rich vapor stream, or aportion thereof.

The fermentation inhibitor may be selected from the group consisting ofacetic acid, formic acid, formaldehyde, acetaldehyde, lactic acid,furfural, 5-hydroxymethylfurfural, furans, uronic acids, phenoliccompounds, sulfur-containing compounds, and combinations or derivativesthereof. In some embodiments, the fermentation inhibitor comprises orconsists essentially of acetic acid.

In the case of acetic acid, the stripped liquid stream preferably hasless than 10 g/L acetic acid concentration, such as less than 5 g/Lacetic acid concentration. The rectification column vapor streampreferably has less than 0.5 g/L acetic acid concentration, such as lessthan 0.1 g/L acetic acid concentration. The rectified liquid streampreferably has at least 25 g/L acetic acid concentration, such as about40 g/L or more acetic acid. In some embodiments, the rectified liquidstream has at least 10 times higher concentration of acetic acidcompared to the stripped liquid stream. In certain embodiments, theprocess further comprises recovering the acetic acid contained in therectified liquid stream using liquid-vapor extraction or liquid-liquidextraction.

In some embodiments, the water-rich liquid stream includes evaporatorcondensate. The evaporator condensate may be derived from an evaporatorin which biomass solids are concentrated, and the biomass solids may bederived from the same biomass feedstock as the biomass-derived liquidhydrolysate, in an integrated process.

Optionally, the fermentation inhibitor (e.g., acetic acid) is recycledto a previous unit operation for generating the biomass-derived liquidhydrolysate stream, to assist with hydrolysis or pretreatment of abiomass feedstock or component thereof.

The process may be continuous, semi-continuous, or batch. Whencontinuous or semi-continuous, the stripping column may be operatedcountercurrently, cocurrently, or a combination thereof Therectification column may be operated continuously or in batch.

In various embodiments, step (g) comprises compressing and/or conveyingthe rectification column vapor stream using a device selected from thegroup consisting of a mechanical centrifugal vapor compressor, amechanical axial vapor compressor, a thermocompressor, an ejector, adiffusion pump, a turbomolecular pump, and combinations thereof.

If desired, a base or other additive may be included in the water-richliquid stream, or separately introduced to the rectification column, toproduce salts or other reaction products derived from fermentationinhibitors. In some embodiments, the water-rich liquid stream includesone or more additives capable of reacting with the fermentationinhibitor. In certain embodiments, the fermentation inhibitor includesacetic acid, and the one or more additives include a base. An acetatesalt may then be generated within the rectification column, or in a unitcoupled to the rectification column. Optionally, the acetate salt may beseparated and recovered using liquid-vapor extraction or liquid-liquidextraction.

A product-by-process is provided by the present invention. That is, someembodiments provide a product, such as ethanol, produced by any of thedisclosed processes.

It should be noted that some embodiments utilize a business system inwhich steps of a selected process are practiced at different sites andpotentially by different corporate entities, acting in conjunction witheach other in some manner, such as in a joint venture, an agencyrelationship, a toll producer, a customer with restricted use ofproduct, etc. For example, biomass may be digested and refined byhydrothermal-mechanical steps as described herein, and the refinedcellulose-rich solids may be transported to another site for enzymatichydrolysis to sugars and then fermentation to ethanol. Or the biomassmay be digested and refined by hydrothermal-mechanical steps andhydrolyzed by enzymes, and then the hydrolysate is transported toanother site (such as a first-generation ethanol plant) to be fermentedto ethanol.

Some variations of the invention are known as GreenPower3+® technologyor GP3+® technology (trademarks of API Intellectual Property Holdings,LLC), commonly assigned with the assignee of this patent application.

In this detailed description, reference has been made to multipleembodiments of the invention and non-limiting examples relating to howthe invention can be understood and practiced. Other embodiments that donot provide all of the features and advantages set forth herein may beutilized, without departing from the spirit and scope of the presentinvention. This invention incorporates routine experimentation andoptimization of the methods and systems described herein. Suchmodifications and variations are considered to be within the scope ofthe invention defined by the claims.

All publications, patents, and patent applications cited in thisspecification are herein incorporated by reference in their entirety asif each publication, patent, or patent application were specifically andindividually put forth herein.

Where methods and steps described above indicate certain eventsoccurring in certain order, those of ordinary skill in the art willrecognize that the ordering of certain steps may be modified and thatsuch modifications are in accordance with the variations of theinvention. Additionally, certain of the steps may be performedconcurrently in a parallel process when possible, as well as performedsequentially.

Therefore, to the extent there are variations of the invention, whichare within the spirit of the disclosure or equivalent to the inventionsfound in the appended claims, it is the intent that this patent willcover those variations as well. The present invention shall only belimited by what is claimed.

EXAMPLE

Corn stover is subjected to the process according to some embodiments.The composition of the corn stover is as follows:

Glucan 42.9 wt %

Xylan 21.2 wt %

Galactan 1.2 wt %

Arabinan 2.2 wt %

Mannan 0.2 wt %

Lignin 23.4 wt %

Ash 3.1 wt %

The cook (digestor) conditions include a digestor temperature of 183° C.and a digestor residence time of 22 minutes. Following the chemicalreaction in the digestor, light mechanical refining is carried out onthe digested material, without separation of solid and liquid. Themechanical refining employs an atmospheric bench refiner (0.5 mm gap, 1pass).

The digested material is then subjected to enzymatic hydrolysis. Theslurry concentration is about 10 wt % total solids. A commerciallyavailable cellulase enzyme cocktail is used, at an enzyme dose of 2.25wt % on biomass. The pH during enzymatic hydrolysis is in the 4.8-5.3range. The temperature during enzymatic hydrolysis is 54° C., and thehydrolysis is carried out for 72 hours to obtain a liquid hydrolysate.

The liquid hydrolysate is then fermented using a commercially availableethanol-producing yeast. The initial pitch is 0.4 g dry yeast per literof the time-final fermentation broth. Fed-batch fermentation isemployed, with a 20-hour feed time. The total fermentation time is 36hours, including the fed-batch fill time. Ammonia base is used and thepH is controlled to 6.0. No fermentation nutrients are added duringfermentation.

The liquid hydrolysate is fermented to ethanol with 82% theoreticalfermentation yield, based on total monomers in the liquid hydrolysatefed to the fermentor. The calculated yield of ethanol is this experimentis about 57 gallons ethanol per dry ton of starting biomass (cornstover).

What is claimed is:
 1. A process to produce ethanol from lignocellulosicbiomass, said process comprising: (a) introducing a lignocellulosicbiomass feedstock to a single-stage digestor, wherein said feedstockcontains cellulose, hemicellulose, and lignin; (b) exposing saidfeedstock to a reaction solution comprising steam or liquid hot waterwithin said single-stage digestor, to solubilize at least a portion ofsaid hemicellulose in a liquid phase and to provide a cellulose-richsolid phase; (c) enzymatically hydrolyzing said cellulose-rich solidphase in a first hydrolysis reactor configured for celluloseliquefaction, thereby providing a first hydrolyzed cellulose mixturecontaining said liquid phase; (d) refining said first hydrolyzedcellulose mixture in a mechanical refiner to reduce average particlesize of said first hydrolyzed cellulose mixture, thereby providing asecond hydrolyzed cellulose mixture; (e) enzymatically hydrolyzing saidsecond hydrolyzed cellulose mixture in a second hydrolysis reactorconfigured for cellulose saccharification, thereby generatingfermentable sugars, wherein said second hydrolysis reactor includes aself-cleaning filter to remove cellulosic fiber strands; (f) recyclingat least a portion of said cellulosic fiber strands back to said firsthydrolysis reactor and/or to said mechanical refiner; and (g) fermentingat least some of said fermentable sugars in a fermentor to produceethanol.
 2. The process of claim 1, wherein said lignocellulosic biomassfeedstock is selected from the group consisting of hardwoods, softwoods,sugarcane bagasse, sugarcane straw, energy cane, corn stover, corn cobs,corn fiber, and combinations thereof
 3. The process of claim 1, whereinsaid lignocellulosic biomass feedstock is pretreated, prior to step (a),using one or more techniques selected from the group consisting ofcleaning, washing, presteaming, drying, milling, particlesize-classifying, and combinations thereof.
 4. The process of claim 1,wherein at least a portion of said reaction solution is introduced tosaid feedstock in a pre-impregnator prior to step (b).
 5. The process ofclaim 1, wherein step (b) includes a digestor residence time from about2 minutes to about 4 hours.
 6. The process of claim 1, wherein step (b)includes a digestor temperature from about 150° C. to about 220° C. 7.The process of claim 1, wherein step (b) is conducted at a digestorliquid-solid weight ratio from about 1 to about
 4. 8. The process ofclaim 1, wherein step (b) is conducted at a digestor pH from about 3 toabout
 5. 9. The process of claim 1, wherein said reaction solutionfurther comprises acetic acid.
 10. The process of claim 1, wherein vaporis separated from said liquid phase prior to step (c).
 11. The processof claim 10, wherein heat is recovered from at least some of said vapor.12. The process of claim 10, wherein at least some of said vapor iscondensed or compressed and returned to said digestor.
 13. The processof claim 1, wherein said mechanical refiner is selected from the groupconsisting of a hot-blow refiner, a hot-stock refiner, a blow-linerefiner, a disk refiner, a conical refiner, a cylindrical refiner, anin-line defibrator, an extruder, a homogenizer, and combinationsthereof.
 14. The process of claim 1, wherein said second hydrolysisreactor is a multiple-stage hydrolysis reactor.
 15. The process of claim1, wherein said self-cleaning filter is disposed between two stages ofsaid multiple-stage hydrolysis reactor.
 16. The process of claim 1,wherein step (e) includes enzymatic hydrolysis of hemicelluloseoligomers to generate fermentable monomer sugars.
 17. The process ofclaim 16, wherein at least a portion of said fermentable monomer sugarsare also fermented to produce said ethanol.
 18. The process of claim 1,said process further comprising concentrating said ethanol bydistillation.
 19. An ethanol product produced by a process according toclaim
 1. 20. An ethanol product produced by a process according to claim18.